when a diagnostic is an extension and has no other -W flag, 
indicate that it was enabled with -pedantic so people know
why they're getting them:

$ printf "int x;" | clang -xc - -pedantic
<stdin>:1:7: warning: no newline at end of file [-pedantic]
int x;
      ^



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96365 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/TextDiagnosticPrinter.cpp b/lib/Frontend/TextDiagnosticPrinter.cpp
index 9ec5ffe..3c64332 100644
--- a/lib/Frontend/TextDiagnosticPrinter.cpp
+++ b/lib/Frontend/TextDiagnosticPrinter.cpp
@@ -786,12 +786,15 @@
   llvm::SmallString<100> OutStr;
   Info.FormatDiagnostic(OutStr);
 
-  if (DiagOpts->ShowOptionNames)
+  if (DiagOpts->ShowOptionNames) {
     if (const char *Opt = Diagnostic::getWarningOptionForDiag(Info.getID())) {
       OutStr += " [-W";
       OutStr += Opt;
       OutStr += ']';
+    } else if (Diagnostic::isBuiltinExtensionDiag(Info.getID())) {
+      OutStr += " [-pedantic]";
     }
+  }
 
   if (DiagOpts->ShowColors) {
     // Print warnings, errors and fatal errors in bold, no color